In a sand casting process of an internal combustion engine cylinder block, an expendable mold package is assembled from a plurality of resin-bonded sand cores that define the internal and external surfaces of the engine block. Typically, each of the sand cores is formed by blowing resin-coated foundry sand into a core box and curing it therein.
Traditionally, the mold assembly method involves positioning a base core on a suitable surface and building up or stacking separate mold elements to shape such casting features as the sides, ends, valley, water jacket, cam openings, and crankcase. Additional cores may be present as well depending on the engine design.
Removal of thermal energy from the liquid metal in the mold package is an important consideration in the foundry process. Rapid solidification and cooling of the casting promotes a fine grain structure in the metal leading to desirable material properties such as high tensile and fatigue strength, and good machinability.
For engine designs with highly stressed bulkhead features, the use of a thermal chill may be necessary. The chill is much more thermally conductive than foundry sand and readily conducts heat from those casting features it contacts. The chill consists of one or more steel or cast iron bodies assembled in the mold in a manner to shape some portion of the features of the casting. A crankcase chill is typically placed into the base core tooling and a core formed about them, or they may be assembled into the base core or between the crankcase cores during mold assembly.
Windows are added to a bulkhead to improve breathing or airflow from bay to bay in the engine cylinder block, or to remove a very thin wall condition. In some cases, holes are drilled through the bulkheads to provide the bay to bay breathing. However, since the bulkhead is one of the most highly stressed portions of an engine cylinder block, extreme care must be used when designing and manufacturing the windows to avoid unintended stress concentrating anomalies.
It would be desirable to produce a cylinder block casting having a window formed in a bulkhead thereof, wherein the peak mechanical stresses present in the bulkhead are minimized and not unintentionally concentrated, and casting efficiency and casting accuracy are maximized.